At present, conventional x-ray mammography continues to be a gold standard for breast cancer screening. However, there has been growing interest in the use of other imaging modalities in conjunction with mammography in order to improve the sensitivity for detection of early malignancies and to reduce the false positive rates. Breast ultrasound (US) and contrast-enhanced magnetic resonance imaging (CE-MRI) are currently being used in this role, while other modalities including x-ray tomosynthesis, nuclear medicine, optical techniques, and acousto-optical techniques are under development. However, the type of breast support used in mammography, namely vigorous compression between two flat surfaces, is either incompatible with or suboptimal for the majority of these upcoming imaging modalities. As an example, the dual modality tomosynthesis (DMT) scanner, located at the University of Virginia Breast Care Center, performs both x-ray breast tomosynthesis (XBT) and molecular imaging breast tomosynthesis (MBIT) with the breast in a single configuration in order to assure that accurate co-registration can be obtained between the two resulting 3-D image sets. Both XBT and MBIT use a tomosynthesis image acquisition approach, in which multiple views of the breast are obtained over a range of viewing angles. XBT provides anatomical information and can reliably resolve objects on a sub-millimeter scale. MBIT provides functional information through the use of an intravenously injected tracer tagged with a radioisotope and has spatial resolution on the order of 2.5 to 5.0 mm. Preliminary human studies have demonstrated that the addition of MBIT to XBT can improve negative predictive value, specificity, and overall accuracy.
A significant issue in mammography can be obscuration of malignancies by superimposed normal breast tissue in the image. Superimposition is especially problematic for the estimated 40-60% of women whose breasts are categorized as radiodense. It is, in part, for this reason that in mammography the breast is flattened by compressing it between a flat breast support (usually the top surface of the detector assembly) and a flat compression paddle using a large (up to and potentially exceeding 40 pounds) compressive force. With regards to DMT scanning, the use of XBT reduces the ramifications of tissue overlap by generating 3-D images that can be viewed as thin slices, thereby substantially reducing the amount of clutter in each image slice compared to that in a mammographic image, which can sum all the healthy background tissue into one image.
Accordingly, there is a need for a new breast immobilization technique whose design is not constrained by the requirements of mammography and that could improve both image quality and patient comfort.